As we mentioned on the previous page, NASCAR drivers love the groove because it follows the most efficient path around the track. Since most NASCAR tracks are oval, you might think that any path around them is the same length, but that's not actually true. Think of a track and field race. A long distance track and field race has what is referred to as a staggered start; the runners in the outside lanes start in front of the runners in the inside lanes. The staggered starting positions make up for the extra distance the outside runners will have to cover because the outside lanes are slightly longer than the inside lanes.
That doesn't mean that all racetrack grooves hug the inside of the track. In racing, any time spent slowing down is time lost, so race car drivers don't like to have to slow down as they enter the turns. Hugging the inside of a turn would require a driver to do just that. To avoid having to slow down for a turn, a race car driver will use the whole track -- entering the turn wide, but then cutting in close to the inside edge at the last possible second. While this strategy may lead to the car covering a slightly longer distance, the car can cover that distance much faster than it could cover the shorter, inside distance if the driver had to apply the brakes for each turn. Often, a NASCAR race car on an oval track can remain at or near full throttle for the entire lap.
What makes the groove depends on how the individual track is constructed. NASCAR tracks have banked curves. That means the track surface tilts inward, toward the center of the track; the banking runs perpendicular to the direction the cars are moving. Banking the curves allows the cars to really attack them without having to slow down. In fact, going too slowly on a steep-banked curve can spell trouble. The banking allows the cars to slingshot around the curve. Where the groove is located, as well as how many grooves there are -- remember, some tracks have more than one -- depends on how steep the particular curve is banked.
On the next page, find out what happens when a driver ends up outside of the groove.